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Car Junkie
Join Date: Sep 2002
Location: Dallas, Texas
Posts: 76
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Three Ring Circus - Timing, Idle, and Mixture
So I rebuilt my distributor and put it back in the car last night. I was careful to orient it back in the way it was previously at TDC, and the car fired right up. Super, success in that department. So then I go to monkey with the timing and idle. FYI, the car is a late '83 SC with a disconnected O2 sensor (otherwise stock CIS), SSI's and no cat. Here's what I did based on the instructions in Bentley and 101 Projects:
1) Start car and let warm up to operating temperature. 2) Adjust idle to 950 rpm by the large screw on the throttle body WITH the vacuum lines on the distributor CONNECTED. 3) Disconnect vacuum lines and the idle speed jumps considerably to 1500-1700 rpm. Adjust timing to 5 degrees at the now higher idle. 4) Reconnect vacuum lines, the idle drops to 400 rpm and it runs like crap. I thought that I did this according to instructions, but obviously I did something wrong. My questions are these: 1) What did I miss? 2) Is Bentley's instruction of disconnecting the vacuum advance bogus? 3) Should I reconnect my O2 sensor for all of this? 4) Is it critical to have both the 5 degrees at idle and the 23 degrees at 6000rpm? It would seem as though changing the 6k setting would affect the idle setting. Is the 6k measure a check figure only to see if the distributor is seeing full advance? I didn't mess with the mixture after failing to achieve the correct timing and idle. How much more complication will mixture changes add to the circus? Thanks! Cheers, Brad '83 SC Coupe |
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08-27-2003, 11:35 AM
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Registered
Join Date: Feb 2003
Location: Aurora, CO
Posts: 822
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Brad, for one thing it's odd that your idle jumps that high when you've disconnected the vacuum lines and plugged them (I assume). The timing is not meant to be set at 1500-1700 rpms and the tech specs say to set it at full advance even though I see alot of people who will set it at idle. I've never disconnected my o2 sensor for timing adjustment. If you did not plug your vacuum line, do that and try it again. Good luck!
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Matt '82 911SC Targa! |
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08-27-2003, 11:47 AM
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Registered
Join Date: Aug 2003
Location: San Mateo, CA
Posts: 225
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Another Brad with an SC coupe here (though my SC is 1 year older than yours).
I'm in the process of properly tuning my timing, idle and mixture as well. My idle also jumps up when I disconnect the vacuum retard. It is my understanding that this is normal for this vintage distributor. -Brad
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'82 911SC Coupe |
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08-27-2003, 12:09 PM
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Registered
Join Date: Apr 2003
Location: Las Cruces, NM
Posts: 2,459
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When you disconnect them, you have to plug them up as well otherwise you just created a massive vacuum leak.
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2007 Mazda 3 hatch 1972 Porsche 914 roller with plenty of holes to fix 
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08-27-2003, 01:07 PM
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Registered
Join Date: Apr 2003
Location: Orange County, California
Posts: 337
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I believe this is the correct way to set the timing...stolen from John Walker...
1. Start and allow car to get warm 2. Disconnect vacuum lines and plug both....idle will increase (normal) 3. Set Idle to 950 4. Time The difference was adjusting the idle down with the vacuum lines off and plugged... down to 950......Ofcourse after you have timed , plug vac lines back in.....adjust your idle up back to 950, again Have I learned anything yet? 
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Mike 83 SC |
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08-27-2003, 09:50 PM
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